British forces have stormed the headquarters of a rogue Iraqi police unit where it was feared that police officers planned to kill detainees, a military spokesman has said.

Seven Iraqis were killed when about 1,000 British soldiers carried out the pre-dawn raid in southern Basra.

The police station was demolished with explosives afterwards.

Major Charlie Burbridge said: "There are 178 prisoners inside the police station and one of the reasons we decided to go today was that we began to receive some very accurate intelligence which suggests that the serious crime unit was about to start killing the prisoners."

A British force of Challenger tanks and Warrior armoured fighting vehicles came under rocket-propelled grenade and machinegun fire from alleyways as it approached the station, he said.

Torture

Burbridge said many of the prisoners held by the Serious Crimes Unit had been tortured.

"The prisoners were found with signs of torture, such as crushed hands, cigarette burns, scars from electric shock treatment and many couldn't walk," he told Al Jazeera.

Captain Tane Dunlop, another British military spokesman, said the troops carried out medical assessments of detainees at the building and transferred them to another police station.

"We [then] used explosives to put the building beyond use so it can no longer be used by the criminal enterprise," he said. "We had clear directions from the prime minister and governor [Mohammed] Waili to dissolve the unit."

"The president is unhappy. He is talking to the Americans about it as we speak," he added.

Othman said the Iranian diplomats came to Iraq at the invitation of the Iraqi leader but he was not aware if they had met with him.

"The invitation was within the framework of an agreement between Iran and Iraq to improve the security situation."

A senior official told the New York Times Monday that the US military was holding at least four Iranians, including senior military officials, who were seized in two raids last week despite having papers showing that they were accredited to work in Iraq.

"We conduct operations against those who threaten Iraqi and coalition forces," the official said. "This was based on information."

One official said that "a lot of material" was seized in the raid, but declined to say if it included arms or documents that pointed to planning attacks.

It was yet unclear what kind of evidence US officials had that the Iranians were planning attacks.

One of the raids targeted the car of the two Iranian diplomats while driving to the Iranian embassy to the west of the Tigris River.

Iraqi officials said that the diplomats were stopped after leaving the Buratha mosque.

US soldiers also raided the compound of Shiite leader Abdel-Azia Al-Hakim, leader of the influential Shiite Supreme Council for Islamic Revolution in Iraq (SCIRI).

A number of Iranian officials were nabbed from inside the house of Hadi Al-Ameri, the chairman of the Iraqi Parliament's Security Committee and leader of the Badr Organization, SCIRI's armed wing.

The Badr Organization is accused of condoning a series of sectarian attacks against Sunnis.

Repercussions

US has long accused Iran of interfering in Iraq's internal affairs but has rarely produced evidence

In Tehran, the Foreign Ministry summoned the Swiss ambassador to discuss the arrests with him.

"The Iraqi government is responsible for their release and the occupiers, based on the international rules, should be kept responsible for it too," Foreign Ministry spokesman Mohammad Ali Hosseini said.

"This move is not compatible with any international regulations and will provoke unpleasant repercussions," he warned.

The Swiss embassy has been representing US interests in Iran since diplomatic relations between Tehran and Washington were cut after the 1979 Islamic revolution.

US National Security Council spokesman Gordon D. Johndroe said two diplomats were initially among the group of Iranians arrested.

He said the envoys were turned over to the Iraqi authorities and later released.

Johndroe confirmed that a group of other Iranians, including the military officials, remained in custody while an investigation continued.

However, Talabani's media adviser and an official in the Shiite-dominated government were not aware the diplomats were freed.

"We are only aware of the arrest of the two diplomats," an SCIRI official told Reuters.

"I don't think that there are any military officials. It is awkward that they would be holding military officials," he added.

The SCIR has been in exile in Iran during the reign of ousted Iraqi president Saddam Hussein.

The Bush administration has long accused Iran of interfering in Iraq's domestic affairs but has rarely produced evidence.

The arrests come amid mounting diplomatic tension between Iran, the US after the UN Security Council voted to impose sanctions on Iran's nuclear program.

In response to the vote, Iran defiantly vowed to start work immediately on drastically expanding its capacity to enrich uranium.

Washington accuses Iran of seeking to develop a nuclear weapon, a charge vehemently denied by Tehran, which says it only wants to provide atomic energy to a growing population.